This invention relates to a pyrometallurgical process for treating a feed material.
High temperature smelting processes are examples of pyrometallurgical processes. Such processes are often carried out in two vessels, the one vessel being used to heat the feedstock (feed material) and thereby melt it, and the second vessel being used to oxidise the molten feedstock. The use of two vessels carries with it several disadvantages, one of which is the difficulty of transferring molten feedstock from one vessel to the other.
Lances have been developed in Australia which enable fuel and oxidising gas to be introduced into feedstock for a smelting process. A typical lance of this type is described in Australian Patent No. 520351 and consists of an outer tube and an inner tube. Liquid fuel for the process passes down the inner tube and exits through a nozzle into a mixing zone. In the case of the solid fuel lance, there is no nozzle. Oxidising gas passes along the passage defined between the inner and outer tubes and into the mixing zone. The oxidising gas acts as a coolant for the outer tube. The cooling effect of this gas on the outer tube allows slag or other material which is splashed on to this tube from the molten mass to freeze and so insulate and protect the tube. With the use of this technology, more than one lance is necessary for the melting and oxidation or reduction of the feedstock. These operations can all take place in a single vessel. Further, the use of such a lance produces a jet of fuel/oxidising gas with a result that the molten feedstock is vigorously, and even violently, agitated.
The process described above using the lance of Australian Patent No. 520351 is an "in-bath" process in that the feed material is digested and partially oxidised in the slag which is in a state of high turbulence effected by the injection, at high speed, of oxidising gas from the lance. An "in-flight" process is also known in which feed material in a dry and finely particulate form is combusted in a stream of oxygen-enriched air in a vertical shaft. The products of combustion fall on to a molten bath below where slag and matte fractions separate. Such "in-flight" processes are carried out in large furnaces which are expensive to produce and to operate.